Multifunctional Lipid Multilayer Stamping

1. Omkar A. Nafday¹, 
2. Troy W. Lowry², 
3. Steven Lenhert^1,*

Article first published online: 6 FEB 2012

DOI: 10.1002/smll.201102096

Nanostructured lipid multilayers on surfaces are a promising biofunctional nanomaterial. For example, surface-supported lipid multilayer diffraction gratings with optical properties that depend on the microscale spacing of the grating lines and the nanometer thickness of the lipid multilayers have been fabricated previously by dip-pen nanolithography (DPN), with immediate applications as label-free biosensors. The innate biocompatibility of such gratings makes them promising as biological sensor elements, model cellular systems, and construction materials for nanotechnology. Here a method is described that combines the lateral patterning capabilities and scalability of microcontact printing with the topographical control of nanoimprint lithography and the multimaterial integration aspects of dip-pen nanolithography in order to create nanostructured lipid multilayer arrays. This approach is denoted multilayer stamping. The distinguishing characteristic of this method is that it allows control of the lipid multilayer thickness, which is a crucial nanoscale dimension that determines the optical properties of lipid multilayer nanostructures. The ability to integrate multiple lipid materials on the same surface is also demonstrated by multi-ink spotting onto a polydimethoxysilane stamp, as well as higher-throughput patterning (on the order of 2 cm² s⁻¹ for grating fabrication) and the ability to pattern lipid materials that could not previously be patterned with high resolution by lipid DPN, for example, the gel-phase phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or the steroid cholesterol.

Zhe Jiang†, Quan Qing†, Ping Xie†, Ruixuan Gao†, and Charles M. Lieber*†‡

^†Department of Chemistry and Chemical Biology and^‡School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States

Nano Lett., Article ASAP

DOI: 10.1021/nl300256r

Publication Date (Web): February 6, 2012

Semiconductor nanowires and other semiconducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p–n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p–n diodes have been widely studied as photovoltaic devices, their applications as bio/chem sensors have not been explored. Here we demonstrate that p–n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p–n junctions were synthetically introduced at the joints of kinked silicon nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p–n diode. In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p–n junction. High spatial resolution sensing using these p–n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p–n devices. In addition, kinked p–n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p–n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue.

Thermally Induced Structural and Morphological Changes of CdSe/CdS Octapods

1. Bart Goris¹, 
2. Marijn A. Van Huis², 
3. Sara Bals^3,*, 
4. Henny W. Zandbergen⁴, 
5. Liberato Manna⁵, 
6. Gustaaf Van Tendeloo⁶

Article first published online: 31 JAN 2012

DOI: 10.1002/smll.201101897

Branched nanostructures are of great interest because of their promising optical and electronic properties. For successful and reliable integration in applications such as photovoltaic devices, the thermal stability of the nanostructures is of major importance. Here the different domains (CdSe cores, CdS pods) of the heterogeneous octapods are shown to have different thermal stabilities, and heating is shown to induce specific shape changes. The octapods are heated from room temperature to 700 °C, and investigated using (analytical and tomographic) transmission electron microscopy (TEM). At low annealing temperatures, pure Cd segregates in droplets at the outside of the octapods, indicating non-stochiometric composition of the octapods. Furthermore, the tips of the pods lose their faceting and become rounded. Further heating to temperatures just below the sublimation temperature induces growth of the zinc blende core at the expense of the wurtzite pods. At higher temperatures, (500–700 °C), sublimation of the octapods is observed in real time in the TEM. Three-dimensional tomographic reconstructions reveal that the four pods pointing into the vacuum have a lower thermal stability than the four pods that are in contact with the support.

Electrical, Optical, and Docking Properties of Conical Nanopores

Yao-Qun Li†*, Yu-Bin Zheng†, and Richard N. Zare‡*

^† Department of Chemistry, Xiamen University, Xiamen, 361005 China

^‡ Department of Chemistry, Stanford University, Stanford, California 94305-5080, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn300356d

Publication Date (Web): February 3, 2012

Copyright © 2012 American Chemical Society

The diffusion-influenced translocation behavior of individual nanoparticles upon passage through a conical nanopore has been elucidated by using a pressure-reversal, resistive-pulse technique, as reported by Lan and White in this issue of ACS Nano. We outline here some recent progress in conical nanopore analysis, and we present some prospects for future developments. Compared to cylindrical nanopores, the geometric change brought about by tapered nanopores causes a dramatic difference in electrical and optical properties. Such conical nanopores may also be integrated into microfluidic chips to capture cells or nanoparticles, one per nanopore, and then to release them. These advances hold the promise of making conical nanopores useful as highly efficient actuators and sensors.

Massively Parallel Bacterial and Yeast Suspension Culture on a Chip

1. Mingzhe Gan¹, 
2. Yunfang Tang¹, 
3. Yiwei Shu²,
4. Hongkai Wu², 
5. Liwei Chen^1,*

Article first published online: 1 FEB 2012

DOI: 10.1002/smll.201102322

A new microfluidic chip integrated with 120 parallelmicrobial suspension culture units is demonstrated. Various bacterial strains and even yeast can be cultivated on the chip. With a high degree of integration and simple fabrication process, this chip could be a central component for future high-throughput microbial screening and selection systems

Manipulating Protein Conformations by Single-Molecule AFM-FRET Nanoscopy

Yufan He, Maolin Lu, Jin Cao, and H. Peter Lu*

Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn2038669

Publication Date (Web): January 25, 2012

Copyright © 2012 American Chemical Society

Combining atomic force microscopy and fluorescence resonance energy transfer spectroscopy (AFM-FRET), we have developed a single-molecule AFM-FRET nanoscopy approach capable of effectively pinpointing and mechanically manipulating a targeted dye-labeled single protein in a large sampling area and simultaneously monitoring the conformational changes of the targeted protein by recording single-molecule FRET time trajectories. We have further demonstrated an application of using this nanoscopy on manipulation of single-molecule protein conformation and simultaneous single-molecule FRET measurement of a Cy3–Cy5-labeled kinase enzyme, HPPK (6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase). By analyzing time-resolved FRET trajectories and correlated AFM force pulling curves of the targeted single-molecule enzyme, we are able to observe the protein conformational changes of a specific coordination by AFM mechanic force pulling.

Microdroplet Patterning: Designer Hydrophilic Regions Regulate Droplet Shape for Controlled Surface Patterning and 3D Microgel Synthesi

1. Matthew J. Hancock^4,†, 
2. Fumiki Yanagawa^4,†, 
3. Yun-Ho Jang⁴, 
4. Jiankang He^4,5, 
5. Nezamoddin N. Kachouie⁴, 
6. Hirokazu Kaji^4,6, 
7. Ali Khademhosseini^1,2,3,4,*

Article first published online: 30 JAN 2012

DOI: 10.1002/smll.201290019

The cover image shows how the shape of micro- and nanodroplets can be controlled by patterning surfaces with special hydrophilic regions surrounded by hydrophobic boundaries. Shaped droplets may be used as a simple tool to controllably pattern planar surfaces with microparticles and cells. Under spiral droplets, a gradient deposition pattern is observed. Shaped droplets of prepolymer solution may also be crosslinked to synthesize microgels with tailored 3D geometry. Finite element simulations provide a design platform by linking the shape of the hydrophilic regions to that of the droplets, microgels, and particle deposition patterns.